In the packaging industry, folding cartons are generally manufactured on a production line by folding and gluing carton blanks using a machine often called a folding-gluing machine. Folding cartons are usually produced as a continuous flow coming out of the outlet of a folding-gluing machine. The cartons then in a flat configuration, namely that the various panels of each carton are folded to essentially eliminate the entire internal volume thereof, thereby minimizing the space prior to initial use. Each flat-disposed carton has a length, a width and a thickness, the thickness being significantly less than the length and the width.
Folding cartons are generally arranged in an overlapping manner on a conveyor, usually a horizontally-disposed conveyor belt, which receives the cartons on its upper surface as it advances. Overlapping is done by partially placing the cartons on top of one another in the travel direction.
The flow of overlapping cartons forms what is called a shingled stream. A shingled stream includes a plurality of overlapping flat-disposed cartons. The shingled stream at the outlet of the folding-gluing machine is called the initial shingled stream. The initial shingled stream can be continuous or discontinuous. The initial shingled stream is discontinuous when two successive cartons therein are spaced apart from one another.
The folding cartons in flat configuration often have a non-uniform thickness. Some carton parts may be thicker than others. The maximum thickness is then often in the widthwise direction of the flat-disposed folding cartons. However, variants are possible. In any case, thickness variations complicate handling of cartons, in their transportation and storage in a container prior to the first use, for instance at the time when the cartons are unfolded to create a load volume. In the meantime, cartons remain in a flat configuration.
The maximum thickness is often along the edge corresponding to the bottom part of the unfolded carton, thus the part which is to become the bottom of the unfolded carton in use. During manufacturing, these folding cartons then output the folding-gluing machine in flat configuration and are oriented so that the leading edge, which is transversal to the travel direction, is the edge with the maximum thickness. The cartons are thinner at the transversal trailing edge. The folding cartons are then all identically oriented, which is not advantageous when the cartons must be stacked into batches. Each batch includes a certain number of cartons that may or may not be attached after stacking, for instance by a packaging machine. If there is a thicker edge on one of the sides, the symmetry of the batches will be affected and this will thus complicate batch stacking in view of transportation and storage of these batches. The solution is to alternate the relative direction of the cartons, for instance within the same batch, or from one batch to another, in order to optimize the space occupied by the cartons in a container. The relative repositioning from one carton to another is often called “inversion”.
The folding cartons can be inverted manually but mechanical systems for repositioning them exist. These systems are, however, subject to challenges inherent to this type of operation. For example, known systems generally involve curves in the vertical plane that bend the cartons during in operation. This often makes it impossible to use the system with objects that are inflexible when in a flat configuration. Cartons made of corrugated cardboard or microflute cardboard are examples of objects that are inflexible in a flat configuration because they are made of a more rigid material than flat cardboard. Some microflute cardboard cartons can be damaged when subjected to even a slight bending beyond a critical angle, often less than 2 degrees from the median plane of the carton, thereby causing a permanent and generally aesthetically undesirable deformation on at least one of the major sides of the carton. These objects can be said to have a critical flexibility. Their handling in known systems would require dimensions that would be much too large, at least from a practical point of view, to keep the curvatures under their maximum bending angle. Still, the floor space in most factories is often not large enough to accommodate the required dimensions. On the other hand, it would be difficult, or even impossible, to modify an existing system designed for somewhat flexible objects in a flat configuration so as to handle inflexible objects in a flat configuration. Hence, the versatility of known systems is often limited.
Another challenge with systems for mechanically inverting cartons is their operating speed. The systems must be able to handle objects at the highest possible rate so as to optimize production and synchronize all operations. Increasing operating speeds is always desirable.
The following documents present different approaches for the repositioning objects, for instance folding cartons: EP 1 179 502; EP 1 657, 200; EP 2 230 204, U.S. Pat. No. 3,738,644; U.S. Pat. No. 4,678,172; U.S. Pat. No. 5,078,250; U.S. Pat. No. 5,158,278; U.S. Pat. No. 5,396,752; U.S. Pat. No. 7,360,636; U.S. Pat. No. 8,443,957; US-2003/116476; US-2005/061627; US-2005/285332; US-2012/000748; WO 2009/110979.
Despite what has been proposed over the years, improvements in this technical field are still, and continually, necessary.